247 
Helvetia crispa , Fries . 
but had little success, owing to the difficulty experienced in obtaining early 
stages. His work has recently been supplemented by McCubbin (11), who 
has described the morphology and development of the ascocarp of Helvetia 
elastica , a form with which Helvetia crispa has certain points in common. 
In H. elastica there is a very marked difference between the fertile and 
vegetative hyphae, the former containing several nuclei in each cell, and the 
latter only two. In H. crispa , although there is generally a difference in 
the size of the hyphae, the number of nuclei is so variable that no definite 
separation can be based upon it. 
Proliferation of the penultimate cell to form another hook, a phe- 
nomenon previously observed in Humaria rutilans (7), is described as 
common in Helvetia elastica , and occurs, though less frequently, in H. crispa , 
as does anastomosis of the terminal and stalk cells. An abnormal hypha 
in which the penultimate cell has divided is of interest as the only instance 
observed in this species of an occurrence which appears to be fairly common 
in H. elastica. 
Sexuality. 
Helvetia crispa is another example of the disappearance of normal 
fertilization and its replacement by the fusion of apparently undifferentiated 
nuclei. In this respect it is entirely comparable with Humaria rutilans (7). 
The second fusion occurs in the ascogenous hypha, and, as in the various 
forms already described (7, 8, 9), a double reduction takes place in the ascus. 
Development of the Ascus. 
Harper, in 1905 (10), describes the formation and further development 
of the ascus in Phyllactinia and Erysiphe . In these the ascogenous hypha 
does not bend over, but the same division and fusion of nuclei occurs as in 
the more usual hooked arrangement. In Phyllactinia there is no change in 
the chromosome number throughout the life-history, the chromosomes 
themselves fusing in pairs at nuclear fusion, so that each becomes quadri- 
valent. 
In Humaria rutilans (7) no sexual organs are developed, but fusion of 
vegetative nuclei in pairs occurs. The usual second fusion takes place in the 
formation of the ascus and is followed by a double reduction. The first 
two divisions in the ascus are meiotic, but the third is of a simpler type, in 
which reduction is accomplished without any apparent pairing of the 
chromosomes. Similar processes have been described by Fraser and Wels- 
ford for Otidea aurantia and Peziza vesicidosa (8). In 1909 Fraser and 
Brooks (9) described the cytology of the ascus in Humaria granulata , 
Lachnea ster corea , and Ascobolus furfur aceus, in all of which there is a 
pseudapogamous fusion in the ascogonium and a subsequent fusion in the 
ascus. In each case the double fusion is followed by a double reduction in 
